1. Field of the Invention
The present invention relates to an inline three-beam system color cathode-ray tube electron gun for use with a color cathode-ray tube comprising a color picture tube, a color display device or the like.
2. Description of the Related Art
At present, as the demand for a high-resolution color cathode-ray tube increases, a problem concerning the spot shape of the electron beam at, in particular, a peripheral surface of the screen becomes significant.
Also, a problem occurs in which a difference occurs in focusing voltages among three electron beams at, in particular, the peripheral surface of the screen so that satisfactory spot shapes of the three electron beams cannot be obtained at the same time.
This causes a phenomenon in which red characters become unclear on the right-had side of the screen and blue characters become unclear on the left-hand side of the screen in a display monitor.
In order to solve such problems, there is proposed a color cathode-ray tube electron gun which houses a so-called quadrupole lens.
FIG. 1 shows a diagram of a conventional color cathode-ray tube electron gun housing a quadrupole lens.
This electron gun 70 includes three cathodes KR, KG, KB which are parallely arrayed in an inline-fashion. From the cathodes K (KR, KG, KB) to the anode side, there are coaxially disposed a first electrode 11, a second electrode 12, a third electrode 13, a fourth electrode 14, a fifth electrode 51, 52, a sixth electrode 16 and a shield cap 17, in that order. Then, the fifth electrode is divided by half to provide a first sub-electrode 51 and a second sub-electrode 52. Also, the second electrode 12 and the fourth electrode 14 are connected electrically.
In this color cathode-ray tube electron gun 70, a constant first focusing voltage Ef1 is applied through a stem portion to the third electrode 13 and the sub-electrode 51.
On the other hand, a second focusing voltage Ef2 in which a waveform voltage of a parabolic waveform synchronized with a horizontal deflection is superimposed upon the first focusing voltage Ef1, is applied to the other sub-electrode 52.
Thus, a quadrupole lens (not shows) is formed between the first sub-electrode 51 and the second sub-electrode 52. In addition, this quadrupole lens cases a change of intensity to occur in a focusing lens formed between the sub-electrode 52 and the sixth electrode 16.
As a result, shapes of electron beams at the left and right peripheral portions of the fluorescent screen may be made satisfactory.
Also, FIG. 1 shows the electron gun of a QPF (Quadra Potential Focus) type. The following is also true in bipotential type electron gun without the fourth electrode 14 and a unipotential type electron gun.
Subsequently, FIG. 2 shows a schematic diagram of a color cathode-ray tube.
As shown in FIG. 2, three electron beams R, G, B are emitted from an electron gun 1 and impinge upon the left-hand side of the screen 4 and the right-hand side of the screen at peripheral portions of the fluorescent screen 4. Because these three beams are respectively placed at different positions in a magnetic field of a deflection yoke 2, the directions and intensities of the magnetic field applied to the three electron beams are different.
Accordingly, the distorted states of electron beam spots at the left and right peripheral portions of the fluorescent screen 4 become different in the three electron beams R, G, B. Incidentally, reference number 3 in the figure denotes a glass bulb. Also, xe2x80x9cright-hand side of screenxe2x80x9d and xe2x80x9cleft-hand side of screenxe2x80x9d mean the right-hand side and the left-hand side obtained when the fluorescent screen 4 of the color cathode-ray tube is observed from the outside, respectively.
In general, the focusing voltage or the like is set in such a manner that the spot shape of the center electron beam G of the three electron beams R, G, B becomes optimum.
In this case, when the three electron beams R, G, B impinge upon the right-hand side of the fluorescent screen 4, the red electron beam R passes a relatively outer side of a deflection magnetic field formed by the deflection yoke 2 as compared with the electron beams G and B, and is strongly affected by the deflection magnetic field. As a result, the distortion of the beam spot of the electron beam R on the fluorescent screen 4 becomes larger than that of the other electron beams G, B.
On the other hand, when the three electron beams R, G, B impinge upon the left-hand side of the fluorescent screen 4, the blue electron beam B passes a relatively outer side of the deflection magnetic field formed by the deflection yoke 2 as compared with the electron beams G and R, and is strongly affected by the deflection magnetic field. As a result, the distortion of the beam spot of the electron beam B on the fluorescent screen 4 becomes larger than that of the other electron beams R, G.
Accordingly, in a display monitor, in particular, a large color display monitor having a high resolution, phenomenon, red characters become unclear on the right-hand side screen and blue characters become unclear on the left-hand side screen as mentioned before.
This phenomenon may be expresses such that the respective focusing voltages of the three electron beams R, G, B differ from each other on the peripheral portions of the screen.
For this reason, as a means for solving this problem, there was previously proposed a color cathode-ray tube electron gun for applying lens effects of different intensities to a red electron beam R and a blue electron beam B (see Japanese patent application No. 9-228268, Japanese patent application No. 9-313940, etc.).
FIG. 3 shows an example of an electrode layout of the previously-proposed color cathode-ray tube electron gun mentioned above.
This electron gun 50 includes three cathodes KR, KG, KB that are parallelly arrayed in an inline-fashion. From the cathodes K (KR, KG, KB) to the anode side, there are coaxially disposed a first electrode 11, a second electrode 12, a third electrode 13, a fourth electrode 14, a fifth electrode 51, 52, a sixth electrode 16 and a shield cap 17, in that order. The second electrode 12 and the fourth electrode 14 are electrically connected.
The fifth electrode corresponding to a focusing electrode is halved to provide a first sub-electrode 51 and a second sub-electrode 52. Further, the first sub-electrode 51 is trisected to provide a 5-1Ath electrode 51A, a 5-1Bth electrode 51B and a 5-1Cth electrode 51C.
The 5-1Ath electrode 51A, the 5-1Bth electrode 51B and the 5-1Cth electrode 51C constitute a first quadrupole lens. Also, the 5-1Cth electrode 51C and the 5-2th electrode 52 constitute a second quadrupole lens. Then, the quadrupole lens action of the second quadrupole lens is controlled by the first quadrupole lens.
A fixed focusing voltage Ef1 is applied to the third electrode 13 and the 5-1Ath electrode 51A and the 5-1Cth electrode 51C disposed outside the trisected electrode 51. A third focusing voltage Ef3, in which a waveform voltage (see FIG. 4) of a shape similar to a sawtooth synchronized with a horizontal deflection and the fixed focusing voltage Ef1 are superimposed upon each other, is applied to the 5-1Bth electrode 51B. Also, a second focusing voltage Ef2, in which a waveform voltage (see FIG. 4) of a parabolic shape synchronized with the horizontal deflection and the fixed focusing voltage Ef1 are superimposed upon each other, is applied to the electrode 52.
These three focusing voltages EF1, Ef2, Ef3 are generally applied from a stem portion of the tip end of the electron gun 50.
Incidentally, the waveform of the third focusing voltage Ef3 may be a waveform which linearly changes in the form similar to a sawtooth shown in FIG. 5A or a waveform of a sine wave shape which intermittently occurs once per period of a horizontal deflection period shown in FIG. 5B.
Three electron beam passing apertures are bored through the 5-1Ath electrode 51A, the 5-1Bth electrode 51B, the 5-1Cth electrode 51C, respectively.
In the previously-proposed color cathode-ray tube electron gun described above, by devising the shapes of the electron beam passing apertures of the respective electrodes 51A, 51B, 51C the deflection magnetic fields applied to the three electron beams R, G, B may be independently controlled at the respective electron beams. By independently controlling the deflecting magnetic field, so that differences in the converging effect on the electron beams may be canceled out, three electron beams of satisfactory shapes may be simultaneously obtained at the peripheral portions of the screen, thereby eliminating the phenomenon in which a focusing of red color is deteriorated on the right-hand side of the screen and a focusing of blue color is deteriorated on the left-hand side of the screen.
As a method of devising the shapes of the electron beam passing apertures, there are enumerated the following methods.
1. In the respective electrodes 51A, 51B, 51C, the passing aperture o one outside electron beam (e.g. red R) and the passing aperture of the other outside electron beam (e.g. blue B) are formed as astigmatism shapes different from each other, and the passing apertures of the two outside electron beams (e.g. red R and blue B) of the opposing electrodes are formed as astigmatism shapes different from each other (see FIGS. 12 and 13).
2. In the respective electrodes 51A, 51B, 51C, the passing aperture of one outside electron beam is formed as a large diameter, the passing aperture of the other outside electron beam is formed as a small diameter, and one of the passing apertures the two outside electron beams of the opposing electrodes is formed as a large diameter and the other is formed as a small diameter (see FIGS. 14 and 15).
3. In the respective electrodes 51A, 51B, 51C, a thickness around a passing aperture of one outside electron beam is made large, a thickness around a passing aperture of the other outside electron beam is made thin, a thicknesses around one of the passing apertures of the two outside electron beams of the opposing electrodes is made thick and the other is made thin (see FIGS. 16 and 17).
4. In the above-mentioned arrangement 1, further, by restricting the aspect ratio of the astigmatism shape of the electron beam passing aperture, an influence exerted upon the center electron beam (e.g. green G) may be removed so that a shielding body need not be provided for the center electron beam (see FIGS. 18 and 19).
By adopting the above-mentioned methods, it is possible to independently control the deflection magnetic fields applied to the three electron beams R, G, B at the respective electron beams.
However, according to the above-mentioned methods, if the three kinds of the focusing voltages, i.e. the fixed focusing voltage Ef1, the parabolic-shaped waveform voltage Ef2 and the sawtooth-shaped waveform voltage Ef3 are not adjusted independently, it""s the effect would not be demonstrated sufficiently.
Therefore, as compared with the case in which the two kinds of the focusing voltages Ef1, Ef2 are adjusted like the conventional electron gun shown in FIG. 1, the adjustment process becomes complicated.
The deterioration of the focusing of the red electron beam R and the blue electron beam B at the peripheral portion f the screen is caused by the deflection magnetic field and is separated into a quadrupole lens component and a convergence lens component.
Then, the previously-proposed electron gun mentioned above is able to correct only the quadrupole lens component or to correct only the convergence lens component. Moreover, the above-mentioned electron gun is weak in sensitivity and affects a lens intensity of the other portion. Thus, a complete correction effect cannot be obtained in actual practice.
Therefore, there is required a lens structure having a sufficient correction sensitivity and which may correct both the quadrupole lens component and the convergence lens component of the distortion.
FIG. 6 shows a schematic arrangement of another a conventional display inline-type electron gun.
This electron gun 60 includes three cathodes KR, KG, KB that are parallelly arrayed in an inline fashion. From the cathodes K (KR, KG, KB) to the anode side, there are coaxially disposed a first electrode 11, a second electrode 12, a third electrode 13, a fourth electrode 14, a fifth electrode 51, 52, a sixth electrode 16 and a shield cap 17 in that order.
Also, the second electrode 12 and the fourth electrode 14 are connected electrically.
Then, the third electrode 13 and the fifth electrode 51, 52 are convergence electrodes (hereinafter referred to as focusing electrodes), and held at potentials ranging from 4kV to 10kV.
Also, the sixth electrode is an acceleration electrode, and held at a potential ranging from 20kV to 30kV.
A pre-focus lens is arranged between the cathodes K and the third electrode 13, a first convergence lens (focus lens) is arranged between the third electrode 13 and the fifth electrode 51, 52, and a main convergence lens is arranged between the fifth electrode and the sixth electrode 16.
Then, the third electrode 13 is divided to provide a first sub-electrode 13A and a second sub-electrode 13B, and the fifth electrode is divided by half to provide a first sub-electrode 51 and a second sub-electrode 52.
In this color cathode-ray tube electron gun 60, a constant first focus voltage Ef1 is applied through a stem portion to the electrode 13A on the anode side of the third electrode 13 and the electrode 51.
On the other hand, a second focus voltage Ef2 having a waveform shown in FIG. 7 is applied to the electrode 13B on the anode side of the third electrode 13 and the electrode 52.
This second focus voltage Ef2 has a waveform in which a parabolic waveform synchronized with the horizontal deflection, so-called downwardly-convexed parabolic waveform, is superimposed upon a parabolic-shaped background Eg1 synchronized with a vertical deflection and which becomes a high voltage in a screen corner (corner portion of the screen) and which becomes a low voltage at the center of the screen. Incidentally, the amplitude of this second focusing voltage Ef2 is almost constant.
Thus, variable quadrupole lenses (not shown) are respectively formed between the electrode 13A and the electrode 13B and between the electrode 52 and the electrode 52. In addition, these quadruple lenses cause the change of intensity to occur in a focusing lens (not shown) formed between the electrode 52 and the sixth electrode 16.
As a result, the shapes of the electron beams on the left and right peripheral portions of the fluorescent screen may be made satisfactory.
As already shown in FIG. 2, three electron beams R, G, B emitted from an electron gun 1, which impinge upon the peripheral portions (e.g., the right-hand side and the left-hand side) of the fluorescent screen 4, experience magnetic fields whose directions and intensities are different because the three electron beams are respectively placed at different positions within the magnetic field of a deflection yoke 2.
Accordingly, the distorted states of the electron beam spots on the left and right peripheral portions of the fluorescent screen 4 become different in the three electron beams R, G, B. In FIG. 2, reference numeral 3 designates a glass bulb. Also, xe2x80x9cright-hand sidexe2x80x9d and xe2x80x9cleft-hand sidexe2x80x9d respectively mean the right-hand side and the left-hand side obtained when the fluorescent screen 4 of the color cathode-ray tube is observed from the outside.
In general, the inline-type color cathode-ray tube electron gun 1 is not provided with a mechanism for adjusting convergence of the three electron beams R, G, B on the whole region of the screen and the convergence is adjusted by the deflection yoke 2.
However, recently, there is an increasing demand for such convergence. Also, as resolution becomes high, frequency also increases. Therefore, the conventional convergence adjustment method has difficulty meeting the market""s requirements.
For example, one method of adjusting convergence disposes an electromagnetic coil (so-called neck assembly and coil) on the electron gun side of the deflection Yoke. However, as frequency becomes high, due to the phenomenon of an eddy current which occurs against a deflection magnetic field or the like, a phase difference occurs between a convergence adjustment voltage waveform and the actual scanning so that the voltage waveform has difficulty following the actual scanning. Consequently, a convergence adjustment is difficult such as when a displacement occurs between a desired place to be adjusted and a place that is adjusted in actual practice or the like.
Also, in order to satisfy the high requirements of convergence, the designing of the deflection yoke becomes complicated and a magnetic field arrangement becomes complex with the result that shapes of electron beams on the peripheral portions of the screen tend to be distorted, thereby resulting in focusing characteristics being deteriorated.
In general, in the deflection yoke, when a deflection distortion which causes the shape of the electron beam to be deteriorated is decreased, a magnetic field distribution becomes uniform so that the red electron beam R and the blue electron beam B become coincident with each other on the center of the screen. However, a mis-convergence in a horizontal direction shown in FIG. 8A and a mis-convergence in a vertical direction shown in FIG. 8B occur in the peripheral portions of the screen, thereby resulting in the red electron beam R and the blue electron beam B being displaced from each other.
In order to solve the above-mentioned problems, according to the present invention, in an inline three-beam system color cathode-ray tube, there is provided an inline three-beam systemcolor cathode-ray tube electron gun in which beam spot shapes of three electron beams on left and right end portions of a fluorescent screen may be uniform as much as possible and in which focusing voltages may be adjust with ease.
Also, according to the present invention, in an inline three-beam system color cathode-ray tube, there is provided an inline three-beam system color cathode-ray tube electron gun in which both of a quadrupole lens component and a convergence lens component causing the deterioration of the focusing of the electron beam may be corrected and in which beam spot shapes of three electron beams on the left and right end portions of the fluorescent screen may be uniform as much as possible.
In order to solve the above-mentioned problem, in an inline three-beam system color cathode-ray tube, the present invention includes providing an inline three-beam system color cathode-ray tube electron bun in which the deteriorations of beam spot shapes of the three electron beams on the left and right end portions of the fluorescent screen may be reduced and a satisfactory convergence characteristic may be obtained on the whole region of the screen.
In a color cathode-ray tube electron gun according to the present invention, with trisected focusing electrodes, a voltage of a waveform similar to a sawtooth synchronized with a horizontal scanning is applied to a center focusing electrode, a housed resistor is connected to the center focusing electrode and two outside focusing electrodes, and a voltage which results from passing the voltage of the waveform similar to the sawtooth through the housed resistor is applied to the two outside focusing electrodes.
According to the above-mentioned arrangement of the present invention, because the voltage applied to the two outside electrodes is the voltage which results from passing the voltage of the waveform similar to the sawtooth through the housed resistor and this voltage becomes a voltage of a waveform close to that of a constant voltage, it is possible to obtain effects similar to those obtained when a fixed focusing voltage is applied to the two outside focusing electrodes.
A color cathode-ray tube electron gun according to the present invention may include trisected electrodes, a fixed voltage applied to two outside electrodes of the trisected electrode and, a voltage of a waveform similar to a sawtooth synchronized with the horizontal scanning applied to a center electrode. The center electrode and one outside electrode of the trisected electrodes form a quadrupole lens, and the center electrode and the other outside electrode of the trisected electrodes form a convergence lens./
According to the above-mentioned arrangement of the present invention, because the fixed voltage is applied to the two outside electrodes of the trisected electrodes and the voltage of the waveform similar to the sawtooth synchronized with the horizontal scanning is applied to the center electrode, respectively, the shapes of the electron beams on the peripheral portions of the screen may be made satisfactory.
Further, since the center electrode and one outside electrode form the quadrupole lens and the center electrode and the other electrode form the convergence lens, it is possible to correct both of the quadrupole lens action component and the convergence lens action component of the lens action generated by the deflection magnetic field.
In a color cathode-ray tube electron gun according to the present invention, a voltage of a waveform synchronized with a horizontal direction deflection and a vertical direction deflection is applied to a center electrode of the trisected electrodes comprising a uni-potential lens.
According to the above-mentioned arrangement of the present invention, since the voltage of the waveform synchronized with the horizontal direction deflection and the vertical direction deflection is applied to the center electrode of the trisected electrodes, it is possible to adjust the convergence in the horizontal direction or the vertical direction.